Re: [PATCH 02/28] drm/i915: rework reading pipe disable fuses

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Jun 25, 2019 at 10:54:11AM -0700, Lucas De Marchi wrote:
> This prepares to have possibly more than 3 pipes. I didn't want to
> continue the previous approach since the check for "are the disabled
> pipes the last ones" poses a combinatory explosion. We need that check
> because in several places of the code we have that assumption. If that
> ever becomes false in a new HW, other parts of the code would have to
> change.
> 
> Now we start by considering we have info->num_pipes enabled and disable
> each pipe that is marked as disabled. Then it's a simple matter of
> checking if we have at least one pipe and that all the enabled ones are
> the first pipes, i.e. there are no holes in the bitmask.
> 
> Cc: Jose Souza <jose.souza@intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>

Looks good.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> ---
>  drivers/gpu/drm/i915/intel_device_info.c | 36 +++++++++---------------
>  1 file changed, 13 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_device_info.c b/drivers/gpu/drm/i915/intel_device_info.c
> index 7135d8dc32a7..e64536e1fd1b 100644
> --- a/drivers/gpu/drm/i915/intel_device_info.c
> +++ b/drivers/gpu/drm/i915/intel_device_info.c
> @@ -929,35 +929,25 @@ void intel_device_info_runtime_init(struct drm_i915_private *dev_priv)
>  		}
>  	} else if (HAS_DISPLAY(dev_priv) && INTEL_GEN(dev_priv) >= 9) {
>  		u32 dfsm = I915_READ(SKL_DFSM);
> -		u8 disabled_mask = 0;
> -		bool invalid;
> -		int num_bits;
> +		u8 enabled_mask = BIT(info->num_pipes) - 1;
>  
>  		if (dfsm & SKL_DFSM_PIPE_A_DISABLE)
> -			disabled_mask |= BIT(PIPE_A);
> +			enabled_mask &= ~BIT(PIPE_A);
>  		if (dfsm & SKL_DFSM_PIPE_B_DISABLE)
> -			disabled_mask |= BIT(PIPE_B);
> +			enabled_mask &= ~BIT(PIPE_B);
>  		if (dfsm & SKL_DFSM_PIPE_C_DISABLE)
> -			disabled_mask |= BIT(PIPE_C);
> -
> -		num_bits = hweight8(disabled_mask);
> -
> -		switch (disabled_mask) {
> -		case BIT(PIPE_A):
> -		case BIT(PIPE_B):
> -		case BIT(PIPE_A) | BIT(PIPE_B):
> -		case BIT(PIPE_A) | BIT(PIPE_C):
> -			invalid = true;
> -			break;
> -		default:
> -			invalid = false;
> -		}
> +			enabled_mask &= ~BIT(PIPE_C);
>  
> -		if (num_bits > info->num_pipes || invalid)
> -			DRM_ERROR("invalid pipe fuse configuration: 0x%x\n",
> -				  disabled_mask);
> +		/*
> +		 * At least one pipe should be enabled and if there are
> +		 * disabled pipes, they should be the last ones, with no holes
> +		 * in the mask.
> +		 */
> +		if (enabled_mask == 0 || !is_power_of_2(enabled_mask + 1))
> +			DRM_ERROR("invalid pipe fuse configuration: enabled_mask=0x%x\n",
> +				  enabled_mask);
>  		else
> -			info->num_pipes -= num_bits;
> +			info->num_pipes = hweight8(enabled_mask);
>  	}
>  
>  	/* Initialize slice/subslice/EU info */
> -- 
> 2.21.0
> 
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-- 
Ville Syrjälä
Intel
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